The invention relates to a color display screen, in particular for a color display tube, a color monitor or a plasma display, with a red phosphor and a color pigment.
Color display screens and color monitors are frequently used in bright ambient light. To improve the visibility of the image on the screen under these lighting conditions and to reduce visual fatigue, the display screen should be non-dazzling and exhibit a low reflection and a high contrast.
The contrast can be maximized by increasing the influence of the external light source in comparison with the luminance of the phosphors in the display screen coating. This can be achieved, for example, by means of color filters in the form of inorganic pigments, which color filters are selected so as to be as transparent as possible to the color emitted by the phosphor in question, while they absorb the other spectral components, so that the diffuse reflection of ambient light at the phosphor powder is suppressed.
A color pigment which is suitable for the pigmentation of a phosphor must exhibit absorption properties which correspond to the emission characteristic of the phosphor. In addition, it is required that a pigmentation for phosphor coatings is stable in a vacuum, that electron bombardment or gas discharges do not cause degradation of said pigmentation, that the pigmentation is inert with respect to reducing, oxidizing or hydrolyzing reagents and does not decompose at an increased temperature.
EP-A-0 697 373 discloses color pigments for use in the manufacture of glass colors which can be stoved, and for tinting glazes which can be stoved at temperatures below 700xc2x0 C., as well as for tinting synthetic resins, lacquers and cosmetic articles on the basis of oxide-nitride pigments whose atomic ratio between nitrogen and oxygen determines the color, and which pigments crystallize in the pyrochlore structure of the general formula AxAxe2x80x22xe2x88x92xB2O5+xN2xe2x88x92x or Axe2x80x22B2xe2x88x92yBxe2x80x2yO5+yN2xe2x88x92y, where A, Axe2x80x2, B and Bxe2x80x2 represent one or more cations of the series A: Mg(II), Ca(II), Sr(II), Ba(II), Zn(II); Axe2x80x2: Ln(=trivalent rare earth metal) Bi(III), Al(III), Fe(III); B: V(V), Nb(V), Ta(V), Mo(V), W(V); Bxe2x80x2: Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), Si(IV), Nb(IV), Ta(IV), and x and y represent a number which is greater than or equal to 0 and smaller than 2, with the exception of Ln2Ta2O5N2 or cations crystallizing in the spinel structure and exhibiting the general formula CD2xe2x88x92mDxe2x80x2mO4xe2x88x92mNm or C1xe2x88x92nCxe2x80x2nD2O4xe2x88x92nNn, where C, Cxe2x80x2, D and Dxe2x80x2 represent one or more cations of the series C: Mg(II), Ca(II), Mn(II), Fe(II), Co(II), Ni(II), Zn(II); D: AI(III), Ga(III), In(III), Ti(III), V(III), Cr(III), Ge(III), Co(III), Ni(III); Dxe2x80x2: Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), Si(IV), Nb(IV), Ta(IV); Cxe2x80x2: Al(III), Ga(III), In(III), Ti(III), V(III), Cr(III), Fe(III), Co(III), Ni(III), and m is a number which is greater than 0 and smaller than or equal to 2, and n is a number which is greater than 0 and smaller than or equal to 1, or cations which crystallize in an elpasolite structure and whose general formula can be written as A 2QBO5xe2x88x92zN1+z, where z represents 0, 1 or 2, and if z is equal to 0, Q is a bivalent metal ion C, if z is equal to 1, Q is a trivalent metal ion Axe2x80x3, and if z is equal to 2, Q is a quadrivalent metal ion D in accordance with the formulae Axe2x80x22CBO5N, Axe2x80x22Axe2x80x3BO4N2, Axe2x80x22DBO3N3, where A, B, S and D have the above-mentioned meaning, and Axe2x80x3 represents Ln(III) or Bi(III). EP-A-0697 373 also discloses color pigments with an increased brilliance on the basis of oxide nitrides present in the perovskite structure, their atomic ratio between nitrogen and oxygen being the determining factor for the color, said oxide nitrides being of the general formula A1xe2x88x92uAxe2x80x2uBO2xe2x88x92uN1+u or Axe2x80x2B1xe2x88x92wBxe2x80x2wO1+wN2xe2x88x92w, where A, Axe2x80x2, B and Bxe2x80x2 represent one or more cations of the series A: Mg(II), Ca(II), Sr(II), Ba(II), Axe2x80x2: Ln(III), Bi(III), Al(III), Fe(III); B: V(V), Nb(V), Ta(V); Bxe2x80x2: Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), and u and w represent a number between 0 and 1, whereby, however, for Axe2x80x2 is Ln(III), uxe2x89xa01 and wxe2x89xa0u.
It is an object of the invention to provide a color display screen with a red phosphor and a color pigment, which provides a high-contrast image, exhibits a small reflectance for external light, a high emission luminance and a good emission color quality, and which can be economically manufactured.
In accordance with the invention, this object is achieved by a color display screen comprising a red phosphor and a color pigment having a general formula selected from the group consisting of:
A1xe2x88x92xAxe2x80x2xBO2xe2x88x92xN1+x, where 0 less than x less than 1, A is Mg(II), Ca(II), Sr(II), Ba(II) or Zn(II), Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), B is V(V), Nb(V), Ta(V) or W(V);
AB1xe2x88x92xBxe2x80x2xBO1+xN2xe2x88x92x, where 0 less than x less than 1, A is Mg(II), Ca(II), Sr(II), Ba(II) or Zn(II), Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), B is V(V), Nb(V), Ta(V) or W(V) and Bxe2x80x2 is Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), Si(IV), Nb(IV) or Ta(IV);
AyAxe2x80x22xe2x88x92yB2O5+yN2xe2x88x92y, where 0 less than y less than 2, A is Mg(II), Ca(II), Sr(II). Ba(II) or Zn(II), Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), B is V(V), Nb(V), Ta(V) or W(V);
A2B2xe2x88x92yBxe2x80x2yO5+yN2xe2x88x92y, where 0 less than y less than 2, A is Mg(II), Ca(II), Sr(II). Ba(II) or Zn(II), B is V(V), Nb(V), Ta(V) or W(V), and Bxe2x80x2 is Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), Si(IV), Nb(IV) or Ta(IV);
CD2xe2x88x92mDxe2x80x2mO4xe2x88x92mNm, where 0 less than m less than 2, C is Mg(II), Ca(II), Mn(II), Fe(II), Co(II), Ni(II) or Zn(II) and D is Al(III), Ga(III), In(III), Ti(III), V(III), Cr(III), Fe(III), Co(III) or Ni(III) and Dxe2x80x2 is Ti(IV), Zr(IV), Hf(IV), Sn(IV), Ge(IV), Si(IV), Nb(IV) or Ta(IV);
C1xe2x88x92nCxe2x80x2nD2O4xe2x88x92nNn, where 0 less than n less than 2, C is Mg(II), Ca(II), Mn(II), Fe(II), Co(II), Ni(II) or Zn(II), Cxe2x80x2 is Al(III), Ga(III), In(III), Ti(III), V(III), Cr(III), Fe(III), Co(III) or Ni(III), D is Al(III), Ga(III), In(III), Ti(III), V(III), Cr(II), B Co(III) or Ni(III);
Axe2x80x22CBO5N, where Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), C is Mg(II), Ca(III), Mn(II), Fe(II), Co(II), Ni(II) or Zn(II), B is V(V), Nb(V), Ta(V) or W(V);
Axe2x80x22Axe2x80x3BO4N2, where Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), Axe2x80x3 is trivalent rare earth metal, Bi(III), B is V(V), Nb(V), Ta(V) or W(V); or
Axe2x80x22DBO3N3, where Axe2x80x2 is a trivalent rare earth metal, Bi(III), Al(III) or Fe(III), D is Al(III), Ga(III), In(III), Ti(III), V(III), Cr(III), Fe(III), Co(III) or Ni(III), and B is V(V), Nb(V), Ta(V) or W(V).
A color display screen comprising a red phosphor and one of the above-mentioned oxide-nitride pigments provides a high-contrast, low-reflection image, because, as a result of the mixed-crystal properties of these oxide-nitride pigments, the absorption properties of these pigments can be accurately adapted to the emission spectrum of the phosphor. The absorption edges can be shifted throughout the range of the visible spectrum by choosing the composition, particularly the O/N ratios. In comparison with conventional Fe2O3 pigments, said oxide-nitride pigments are characterized by steeper absorption edges in the yellow-red spectral region and by a high absorbing power. This enables the pigment-containing layers to be thin and the pigment quantities to be small. The oxide-nitride pigments in accordance with the invention can be easily prepared and readily processed in a phosphor composition. They adhere well to the surface of the known red phosphors. They are resistant to electron radiation and gas discharges, and they exhibit a very low vapor pressure, a sufficient temperature resistance up to 700xc2x0 C. and they are not toxic.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.